Thermal switches



C. W. KUHN THERMAL SWITCHES Filed June 17, 1955 l Dec. 8, 1959 United States Patent kO l 'mERMAL SWITCHES Clarence W. Kuhn, Wauwatosa, Wis., assignor to Cutler- Hammer, Inc., Milwaukee, Wis., a corporation of Delaware Application June 17, 1955, Serial No. 516,104

3 Claims. (Cl. 200-113) This invention relates to improvements in thermal switches and in particular to snap-acting thermal switches employing bimetallic actuating elements.

An object of the invention is to fulfill the need for a conveniently mountable thermal switch which operates with a snap action, requires a minimum amount of material and a minimum number of parts and which can be easily manufactured in automatic or non-automatic resetting form.

This andiother objects and advantages of the invention which will hereinafter appear, are realized by the provision of a pair of electrically conductive members mechanically connected together by an electrically insulating material. At least one of the members comprises a bimetallic element which is sprung or polarized so that it will oil can from one position to another in the manner of a Spencer disc as it is heated and cooled. In the cooled condition of the bimetallic element it engages the other member to complete an electrical path through the members in series. When heated by current flow therethrough, the bimetallic member snaps to a position away from the other member to interrupt the circuit.

lCertain embodiments of the invention are shown in the accompanying drawing, it being understood that various modifications are possible to be made in the embodiments illustrated and that other embodiments are possible without departing from the spirit of the invention or the scope of the appended claims.

In the drawing:

Figure 1 is an enlarged top plan view of a thermal switch embodying the invention; y

Fig. 2 is a cross-sectional view taken on line 2-2 of Fig. 1 showing the switch in closed condition;

Fig. 3 is a reproduction of Fig. 2 except that the switch is shown in open position, and

Fig. 4 is a cross-sectional view of an alternative form of switch embodying the invention.

Referring to Figs. 1, 2 and 3 of the drawing, the switch there shown consists of a metallic base disc 10, an active disc 14, an annular ring of insulating material 18, and a pair of contact tips 20 and 22 which are attached to discs and 14, respectively.

Disc 14 is bimetallic. It consists of two layers of metal bonded together and having different thermal expansion characterstics. Extending from one side thereof is an integral lug 16 which facilitates making an electrical connecton to the disc. The base disc 10, like disc 14, is substantially circular. It has an integral mounting and electrical connection lug 12 extending from one side. 'I'he central portion of the disc 10 may be dished or offset laterally, as shown, to accommodate contact tips 20 and 22.

Discs 10 and 14 overlie one another and are held spaced apart by the vitreous enamel insulating ring 18 which is interposed between them along their edges. Vitreous enamel is considered to be an excellent insulating material. It is tired after the discs are positioned and becomes bonded to the discs and holds them rmly inplace. Other materialswhichmechanically join but electrically insulate vthe discs may be employed.

The disc 14 is sprung toward disc 10 so that contacts 20 and 22 are normally engaged "to complete a circuit through the discs. The expansion characteristics of the metals of disc 14 are such that, upon being heated, it is urged away from disc 10. It is sprung so that it will move from disc 10 with a snap action as an incident to heating caused by excessive current flow through the discs and/or excessive temperature of the surrounding atmosphere. Thus it can be used in protecting against excessive ambient temperature rise in enclosed electrical and electronic apparatus or as a current overload switch or both. Moreover, the disc 14 may be sprung so as to be automatically or non-automatically resetting.

Two bimetallic discs 30 and 32 are employed in the switch of Fig. 4. They are held separated by a ring 34 of insulating material and both'discs are sprung inwardly so that their contact tips 36 and 38 normally make electrical contact. In practice one disc will snap at a lower temperature and so only it will be actuated. But in certain instances the use of two sprung discs simplifies production control of unit operating tolerances.

In either switch the contact tips may be dispensed with if the discs are arranged so that they engage one another directly in their closed-switch positions.

If ring 18 in Figs. l, 2 and 3 and ring 34 in Fig. 4 are made continuous, a sealed unit results in which moisture,v

dust and other foreign matter are excluded from the contact area of the discs. If such sealing is not required, the members 10, 14, 30 and 32 need not be circular but simply could be formed in the shape of strips.

I claim:

1. A switch comprising a pair of substantially circular disk-shaped metallic plates overlying one another and held in fixed spaced relationship by an insulating material interposed between them at their edges and to which they are both bonded, at least one of said plates having a portion composed of a plurality of substantially planar layers of metal having different thermal expansion characteristics and being normally sprung into electrical contact at a central point with the other plate to form a conductive path from one plate to the other through said contact, said one plate being so sprung and the expansion characteristics of its layers being such that upon heating of said one plate as an incident to excessive current fiow therethrough or excessively high ambient temperatures, or both, said one plate will be moved out of contact with the other plate with a snap action, and each said plate having a narrowed portion integral therewith and extending therefrom for making an electrical connection thereto.

2. The switch defined in claim 1 in which said plates are solid discs and in which said insulating material comprises a continuous annular ring to form a sealed unit in which foreign matter is excluded from the area of contact between said discs.

3. A switch comprising a part of substantially discshaped metallic members at least one of which is normally sprung at a central point into electrical contact with the other but which members are otherwise held in fixed relationship by an insulating material to which the members are bonded, each of said members having a narrowed portion as a connection means for making electrical connections thereto whereby to complete a circuit through said member at the point of contact, and said one member comprising, at least along the conductive path from said point to its connection means, a plurality of substantially smooth layers of metal having diierent thermal expansion characteristics and being sprung in such manner that upon heating as an incident to ow therethrough df excessive currentor'excessively high ambient temperatures, or both, said centralpoint of said one member will be carried with snap action out of engagement With the other member` References Cited'. in the ileof thisl patent UNITED STATES PATENTS Dixon Nov. 17, 1914 -Mottlau May 26, 1936 

